Segment and Related Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jul. 01, 2012	Apr. 01, 2012	Dec. 31, 2011	Oct. 02, 2011	Jul. 03, 2011	Apr. 03, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment and Related Information [Abstract]
Number of reportable segments	2								2
Segment Reporting Information [Line Items]
Net sales	$ 244,200	$ 250,300	$ 254,000	$ 257,100	$ 251,700	$ 262,200	$ 268,400	$ 262,500	$ 1,005,619	$ 1,044,853	$ 1,002,354
Income (loss) from operations									107,046	97,740	98,849
Restructuring and other charges									0	470	865
Depreciation, depletion and amortization									51,209	58,223	63,981
Segment assets	1,211,189				1,164,955				1,211,189	1,164,955	1,116,100
Capital expenditures									52,130	52,060	34,518
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	160,800	165,600	168,100	167,700	159,900	171,100	171,800	173,300	662,200	676,100	665,000
Income (loss) from operations									84,100	72,800	74,700
Restructuring and other charges										1,000	500
Depreciation, depletion and amortization									10,300	47,600	52,600
Segment assets	617,000				603,800				617,000	603,800	585,700
Capital expenditures									41,000	41,700	23,300
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	83,400	84,700	85,900	89,400	91,800	91,100	96,600	89,200	343,400	368,800	337,400
Income (loss) from operations									32,600	33,200	28,000
Restructuring and other charges										(600)	300
Depreciation, depletion and amortization									40,900	10,600	11,400
Segment assets	355,500				355,800				355,500	355,800	340,500
Capital expenditures									8,000	8,000	8,200
Total Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,005,600	1,044,900	1,002,400
Income (loss) from operations									116,700	106,000	102,700
Restructuring and other charges										500	800
Depreciation, depletion and amortization									51,200	58,200	64,000
Segment assets	972,500				959,600				972,500	959,600	926,200
Capital expenditures									$ 49,000	$ 49,700	$ 31,500